The incandescent bulb has been utilized for over a century. Millions of fixtures using standardized incandescent lamps are in use. The white light LED (Light Emitting Diode) was invented in the early 1990's. Since then, the efficacy of white light LEDs have improved dramatically. Power efficiencies and product life have since surpassed the incandescent bulb. The LED emitted light relative to its cost is currently substantially higher than an incandescent, however.
To efficiently use the higher cost LED light, lenses and reflectors are oven used to direct or guide the light to the intended illumination area. Reflectors and lenses add cost to a LED fixture. LEDs dissipate power and generate heat. For long term reliability and to extend product life, heat must be removed from the LED. A thermal management system, including heat sinking, adds even more cost to a LED fixture.
In new lighting applications the decision to use a LED fixture depends on fixture, installation, and maintenance costs as well as energy savings. The decision to replace or retrofit an incandescent fixture in an existing lighting application may also depend on the original fixture value. Many fixtures have significant value above and beyond replacement costs including sentimental, historical, or architectural. While LED lighting may offer lower energy and maintenance costs, the decision to replace often depends on upfront costs and the capital required.
In many LED fixtures using arrays or multiple LED emitters, emitter “hot spots” (small areas of intense light embedded in a larger area of relative darkness) are visible and cosmetically undesirable. While diffusers may be used, they introduce losses in performance (intensity and other factors).